The Troubles were an ethno-nationalist conflict in Northern Ireland during the late 20th century. Known internationally as the Northern Ireland conflict, it is sometimes described as an "irregular war" or "low-level war"; the conflict began in the late 1960s and is deemed to have ended with the Good Friday Agreement of 1998. Although the Troubles took place in Northern Ireland, at times the violence spilled over into parts of the Republic of Ireland and mainland Europe; the conflict was political and nationalistic, fuelled by historical events. It had an ethnic or sectarian dimension, although it was not a religious conflict. A key issue was the constitutional status of Northern Ireland. Unionists/loyalists, who were Protestants, wanted Northern Ireland to remain within the United Kingdom. Irish nationalists/republicans, who were Catholics, wanted Northern Ireland to leave the United Kingdom and join a united Ireland; the conflict began during a campaign by the Northern Ireland Civil Rights Association to end discrimination against the Catholic/nationalist minority by the Protestant/unionist government and police force.

The authorities were accused of police brutality. Increasing tensions led to severe violence in August 1969 and the deployment of British troops, in what became the British Army's longest operation, they built ` peace walls'. Some Catholics welcomed the army as a more neutral force, but it soon came to be seen as hostile and biased after Bloody Sunday in 1972; the emergence of armed paramilitary organisations led to subsequent warfare over the next three decades. The main participants in the Troubles were republican paramilitaries such as the Provisional Irish Republican Army and the Irish National Liberation Army; the security forces of the Republic of Ireland played a smaller role. Republican paramilitaries carried out a guerrilla campaign against British security forces as well as a bombing campaign against infrastructure and political targets. Loyalists targeted republicans/nationalists and attacked the wider Catholic community in what they described as retaliation. At times, there were bouts of sectarian tit-for-tat violence.

The British security forces undertook both a policing and counter-insurgency role against republicans. There were some incidents of collusion between British security loyalists; the Troubles involved numerous riots, mass protests and acts of civil disobedience and led to segregation and the creation of no-go areas. More than 3,500 people were killed in the conflict, of whom 52% were civilians, 32% were members of the British security forces and 16% were members of paramilitary groups. There has been sporadic violence since the Good Friday Agreement was signed, including ongoing punishment attacks and a campaign by dissident republicans. "The Troubles" refers to the three-decade conflict between unionists. The word "troubles" has been used as a synonym for violent conflict for centuries; the term was used to describe the Irish revolutionary period in the early twentieth century. It was subsequently adopted to refer to the escalating violence in Northern Ireland after 1969; the violence was characterised by the armed campaigns of Irish republican and Ulster loyalist paramilitary groups and British state security forces.

It thus became the focus for the longest major campaign in the history of the British Army. The British government's position is that its forces were neutral in the conflict, trying to uphold law and order in Northern Ireland and the right of the people of Northern Ireland to democratic self-determination. Nationalists regard the state forces as partisan combatants in the conflict; the British security forces focused on republican paramilitaries and activists, the "Ballast" investigation by the Police Ombudsman confirmed that certain British officers colluded on several occasions with loyalist paramilitaries, were involved in murder, furthermore obstructed the course of justice when claims of collusion and murder were investigated. The Troubles were brought to an uneasy end by a peace process that included the declaration of ceasefires by most paramilitary organisations, the complete decommissioning of the IRA's weapons, the reform of the police, the corresponding withdrawal of the British Army from the streets and sensitive Irish border areas such as South Armagh and County Fermanagh, as agreed by the signatories to the Belfast Agreement.

One part of the Agreement is that Northern Ireland will remain within the United Kingdom unless a majority of the Northern Irish electorate vote otherwise. It established the Northern Ireland Executive, a devolved power-sharing government, which must consist of both unionist and nationalist parties. Although the number of active participants was small, the Troubles affected many in Northern Ireland on a daily basis. In 1609, Scottish and English settlers, known as planters, were given land escheated from the native Irish in the Plantation of Ulster. Coupled wit